In general, a fuel cell comprises a cell on which an air electrode layer, an electrolyte layer and a fuel electrode layer are laminated, a fuel supplying part for supplying a fuel as a reducing agent to the fuel electrode layer and an air supplying part for supplying air as an oxidizing agent to the air electrode layer, and it is an electric cell in which electrochemical reaction take place in the cell between the fuel and oxygen in the air to provide electric power to the outside. Fuel cells of various types are developed.
In recent years, because of a rise in consciousness to environmental problems and energy saving, it is studied to use a fuel cell as a clean energy source for various applications. In particular, attentions have been paid to fuel cells which can generate electric power by only supplying directly a liquid fuel comprising methanol and water (refer to, for example, patent documents 1 and 2).
Among them, liquid fuel type fuel cells making use of capillary force for supplying a liquid fuel are known (refer to, for example, patent documents 3 to 7).
Liquid fuel type fuel cells described in the above respective patent documents supply a liquid fuel from a fuel tank to a fuel electrode by virtue of capillary force, and therefore they do not require a pump for sending a liquid fuel with pressure, so that they have merits in reducing a size.
Such liquid fuel type fuel cells as merely making use of capillary force of a porous body and/or a fiber bundle disposed in a fuel reservoir are suited to reduction in a size in terms of constitution, but because a fuel is supplied directly to a fuel electrode in the form of liquid, the fuel follows imperfectly during use over a long period of time under use environment in which it is mounted in a small-sized portable equipment and in which the direction of a cell part are changed constantly in every direction, and the trouble that the fuel is cut off from being supplied is brought about, so that the fuel is interrupted from being supplied constantly to a fuel electrode layer.
On the other hand, known as one of countermeasures for solving the defects is, for example, a fuel cell system in which a liquid fuel is introduced into a cell by virtue of capillary force and in which the liquid fuel is then vaporized in a fuel vaporizing layer and used (refer to, for example, a patent document 8). However, it has the problem that poor followability of the fuel which is a fundamental problem is not improved, and involved therein is the problem that it is difficult to reduce a size of the fuel cell having the above structure because of a system in which a liquid is vaporized and then used as fuel.
As described above, in conventional fuel reservoirs for a fuel cell, the existing situation is that a liquid fuel is instably supplied in supplying the fuel directly to a fuel electrode to cause fluctuation in an output value during operation and that it is difficult to reduce a size thereof to such an extent that they can be mounted in portable appliances while maintaining stable characteristics.
Then, the present applicants filed a patent application of a direct methanol fuel cell in which jointed are plural unit cells each of which is formed by constructing an electrolyte layer on the outer surface of a fuel electrode body comprising a fine porous carbonaceous body and constructing an air electrode layer on the outer surface of the electrolyte layer, wherein a fuel supplying member which is connected with a fuel reservoir for storing a liquid fuel comprising a cartridge structure and which has a penetrating structure is connected with the respective unit cells to supply the liquid fuel (refer to, for example, a patent document 9).
This fuel cell has an excellent function which has never been observed, but involved therein is the problem that when a cartridge type fuel reservoir is heated to be in a high temperature state, boiling, bubbling and spouting of a liquid fuel are brought about a little.
Patent document 1: Japanese Patent Application Laid-Open No. 258760/1993 (claims, examples and others)
Patent document 2: Japanese Patent Application Laid-Open No. 307970/1993 (claims, examples and others)
Patent document 3: Japanese Patent Application Laid-Open No. 66066/1984 (claims, examples and others)
Patent document 4: Japanese Patent Application Laid-Open No. 188008/1994 (claims, examples and others)
Patent document 5: Japanese Patent Application Laid-Open No. 229158/2003 (claims, examples and others)
Patent document 6: Japanese Patent Application Laid-Open No. 299946/2003 (claims, examples and others)
Patent document 7: Japanese Patent Application Laid-Open No. 340273/2003 (claims, examples and others)
Patent document 8: Japanese Patent Application Laid-Open No. 102069/2001 (claims, examples and others)
Patent document 9: Japanese Patent Application Laid-Open No. 63200/2004 (claims, examples and others)